One is not ever going to have good crash protection in an oldie. Adding a roll-cage, etc, won't make up for it. Three-point seatbelts with reinforced mounts are about it along that line. Not trying to rain on the parade, at all, just being "realistic". Best brakes and handling is where that is at, IMO. There's just no way to engineer "crumple zones" into a vehicle that never had them.
To help you imagine the ULTIMATE vintage tow vehicle I know my own. The vintage TV I would best enjoy would be a modified 1967
Imperial . . but the ultimate
would be a DeSoto Suburban
and to do what you propose: perhaps a Cummins 4bt; more realistically a well-warmed V8-383; on a current truck frame to which the old body is adapted and changes made to retain a vintage appearance with up-to-date performance, (such as fully independent suspension and big 4-whl discs). Manual trans and seats that fold out into beds like the original could. A daytripper, not just a TV. And a custom rivetted aluminum roof carrier that complimented the trailer, and a paint job that paid homage to both the car and the trailer. Etc.
But it would be a toy, not a DD; a rolling avatar from The Paradise of Happy Motoring.
Your final sentence includes the word "practical", and I do not find that "ultimate" and "practical" to be together in the same room, much less to dovetail. My daydream TV would cost more than a 2012 top dollar 1T, easily.
"Ultimate" means ignoring time and dollars, no way around it. "Practical" means on-time and under-budget. What you propose will be neither. Better definitions are needed. My last old car (30+ years) was also my daily driver. Just making it new again, and making the relatively minor changes to live in todays traffic was a continual process.
I couldn't sleep tonight so am also reading a thread on restoring a 1970 Ford F250 crew cab with a Cummins 4bt in place of the old V8-390, here.
This sort of thing is not for the faint of heart, and yet this one is relatively easy compared to many others I've seen. But a lot of $$ no matter how you cut it.
Luckily, there are quite a few around here with vintage TV's who'll be along to offer their experience. I do think your trailer is an ideal size (glad it is no bigger, and yet it isn't a beer cooler sized Bambi, either). I look forward to seeing how this comes along.